The present invention relates to bags or packages such as may be formed from plastic film and have an openable mouth and carry a reclosable extruded plastic fastener or zipper inside the mouth. The zipper has complementary profiles separably interlockable in a closed condition of the zipper. Bags or packages of this kind are well known and in widespread use.
In the extrusion of the zipper profiles, especially of the single complementary rib and groove type, due to necessary tolerances it is not feasible to secure a tightly sealing interengagement of the complementary interlock surfaces of the profiles. For many uses, such tolerances are acceptable. However, for some purposes, a thoroughly sealed interlocked relationship of the profiles is desirable.
Heretofore, it has been proposed to attain a sealed condition by applying the zipper strips to the outside of the bag walls and gripping the bag walls within the interlocked zipper strips. Examples of such constructions are found in Danish Pat. No. 90167 of 1961, Norweigan Pat. No. 98822 of 1961, U.S. Pat. No. 3,346,883 and recently issued U.S. Pat. No. 4,703,518. A problem with that construction is that in this fashion it will act to separate the profiles when pressure is transferred onto them by the spreading out of the contents within the bags. Also in many instances the bag sheet material or film will be too thick to be readily gripped within the customary size zipper profiles for bags or package of particular dimensions. An undesirably larger profile structure may be needed to accommodate the bag wall thicknesses, in the grip of the two zipper profiles as is necessary with such a zipper closure scheme. Alternately if the customary size is retained, the bag material may be too thick.
U.S. Pat. No. 2,772,712 is noted as showing narrow zipper profile opening strip clamped between the profiles, but that strip has no sealing function and may actually have the reverse effect i.e. promote leakage by holding the profiles spaced apart adjacent to the narrow strip.